1. Field of the Invention
The present invention relates generally to a composite material bat. More specifically, the bat includes a shell made of multiple layers of unidirectional fiber, wherein the orientation of the fibers increases from a low angle to a high angle from the interior of the shell to the exterior of the shell.
2. Description of Related Art
Diamond sports, such as baseball and softball, typically use bats made of various materials and configurations. Depending on such factors including the regulations of a sport and the gender and age of the players, the size, weight, or dimensions of a bat may also vary. In developing a bat, design considerations include longitudinal stiffness, moment of inertia, mass, and center of gravity. Common materials for bats include wood, plastics, metals, and composites.
Solid wood bats are traditionally used in baseball. Due to impact forces, wood bats are prone to cracking. The wood bats used in baseball are typically constructed of white ash or maple. Wood bats may also be made of hickory and bamboo. Wood bats have become increasingly expensive, causing some baseball leagues to turn to alternative material bats.
Plastic bats are more often used by very young children. For example, plastic bats are used when playing whiffle ball. Plastic bats are designed to withstand the smaller forces exerted by smaller individuals and less rigid, slower moving balls.
Metal bats are typically hollow, tubular, thin-walled shells composed of aluminum or titanium. Metal bats are most commonly used by baseball youth leagues and in fast pitch and slow pitch softball. Metal bats have a tendency to deform in the impact zones due to their thin-walled structure. Once a metal bat is deformed, the trajectory of a ball coming in contact with the bat becomes unpredictable and the bat is typically discarded.
Composite materials can be expensive. Composite materials or composites are materials made from two or more individual materials. When combined, the individual materials retain their own properties. However, the overall composite assumes some combination of the properties of both materials.
Composite materials may be formed of fibers embedded in a matrix. For example, a unidirectional carbon fiber resin matrix composite material is made of carbon fibers embedded within an epoxy resin matrix. The carbon fibers have a high toughness and are typically brittle. The toughness of a material refers to the ability of that material to resist fracture. The brittleness or ductility of a material refers to the tendency of that material to deform prior to fracture. The more brittle a material, the less that material deforms prior to fracture. The more ductile a material, the more that material deforms prior to fracture. Most matrix materials tend to be ductile but not very tough. However, when the epoxy resin and carbon fibers are combined, the composite material may assume an adequate toughness and ductility for use in high impact equipment.
Composite material bats are most commonly used in college softball. Of the materials typically used to construct bats, composite materials allow for the most design flexibility and customization. In other words, longitudinal stiffness, moment of inertia, mass, and center of gravity may be more precisely controlled using such design factors as type of matrix material, type and modulus of the fibers, orientation of the fibers, and number of layers or thickness of the composite.
Composite materials may be isotropic or orthotropic in nature. Isotropic materials have material properties that are independent of the direction of an applied force. In other words, a material property, such as toughness, does not vary if a force is applied longitudinally or axially. Orthotropic materials have material properties that are dependent on the direction of an applied force. Composite materials are typically orthotropic. In other words, a material property, such as toughness, is dependent on the orientation of an applied force. Composite materials having unidirectional fibers embedded in a matrix are orthotropic.
Impact with balls typically cause composite material bats to fail by cracking or breaking. To inhibit failure in composite material devices, manufacturers have taken various approaches. One example is U.S. Pat. No. 5,395,108 to Souders et al. that teaches a layered fiber-reinforced composite material bat made of pre-impregnated (“prepreg”) material. The composite material of the Souders bat includes a braided base layer and additional unidirectional fiber layers that alternate between +/−30 degrees and +/−45 degrees. The braided base layer is composed of fibers that are oriented at 0 degrees and 90 degrees. The additional unidirectional fiber layers alternate in the following manner: +30 degrees, −30 degrees, +45 degrees, −45 degrees, +30 degrees, −30 degrees, +45 degrees, −45 degrees. Each +/−layer combination is a ply, and the bat of Souders et al. uses as many as eight plies.
A second example is U.S. Pat. No. 5,533,723 to Baum that teaches a layered composite material bat including a first sock, a second sock, and an exterior layer made of wood veneer planks. The first sock is comprised of a first layer made of Dupont Kevlar® or S-2 glass fiber with fibers aligned along the longitudinal axis of the bat. The second layer made of graphite is comprised of fibers aligned at a 90 degree angle to the longitudinal axis of the bat. The third and fourth layers are comprised of fibers arrayed at 45 degrees to the fibers of the first two layers. The second sock is constructed similarly to the first sock. However, the second sock includes an additional fiberglass layer with fibers aligned at a 90 degree angle to the longitudinal axis of the bat.
A third example is U.S. Pat. No. RE35081 to Quigley that teaches a layered composite member, such as a sail mast, with high bending strength. The Quigley apparatus includes an innermost ply with unidirectional strands that may be oriented anywhere between +/−30 degrees and +/−90 degrees. A second, adjacent ply has two sets of fibers that are oriented axially along the circumference of the member. The first set of fibers comprises multiple, unbraided, and continuous strips. The second set of fibers comprises multiple braided strips. The second ply is composed of alternating strips of the first and second sets of fibers. Third, fourth, and fifth plies are constructed similarly to the second ply. However, third and fifth plies have fibers that are helically oriented at an angle between +/−5 degrees and +/−60 degrees along the circumference of the member. Similar to the second ply, the fourth ply is axially oriented along the circumference of the member. A final ply of similar construction and fiber orientation as the innermost ply is then applied.
A fourth example is U.S. Pat. No. 6,475,580 to Wright that teaches a method of manufacturing an elongate article such as a golf club shaft. The elongate article is composed of multiple layers of a prepreg composite material. The inner, outer, and interior layers have unidirectional fibers that are aligned with the longitudinal axis of the elongate article. Additional interior layers also have unidirectional fibers oriented between +/−25 and +/−45 degrees with respect to the longitudinal axis of the article.
While the art has addressed many issues related to strength and bending, the challenges of a thick-walled composite shell experiencing repeated impact forces remains unaddressed. In composite material bats, the impact of a ball with the bat tends to cause compression forces on the outermost layers of the bat that shift to tensile forces on the innermost layers of the bat. As a result, many composite bats tend to fail around the edges of the impact zone because the bat is not designed to withstand both compressive and tensile forces. Alternatively, some composite bats may use braided layers, which may be difficult and expensive to manufacture. The use of braided layers may also undesirably increase the weight of the bat.
Therefore, there exists a need in the art for a composite material bat capable of withstanding exterior compressive forces and interior tensile forces to increase durability while effectively managing weight and manufacturing costs.